Passing a knot while belaying

Scenarios: 1) You are toproping a rock climb where the anchor is really high up, and you need to tie two ropes together to make the rope reach the ground.  2) You are belaying a long pitch of easy rock or snow, and have decided to tie two ropes together so your leader can really run it out.  3) You damaged your rope somehow, and you have tied a butterfly knot to isolate the damaged part. In all of these cases, you need to be able to pass the knot through your belay device while keeping the climber safe.  (Note in 2 and 3, the knot will get caught in the first bit of pro the leader has placed.)  Here’s a slick way to do this.

Before the leader leaves the belay, the belayer ties a fig 8 on a bight a few feet below the knot.  The leader can then climb.  When the knot gets close to the belayer, she calls up to the climber to find a balanced stance for a moment.  When the climber is stable, she clips the fig 8 knot onto her harness belay loop with a locking biner.  This keeps the climber safe for a few seconds.  Then, she quickly removes the rope from her belay device and reattaches it past the knot, and then unties the backup knot.

Tips:  Walking backward (if possible) a few steps can help take up the slack.  If the leader is at a tough spot, they can place a bit of solid gear and clip to it during the few seconds they are off belay.